Engines may use a turbocharger to improve engine torque and/or power output density. A turbocharger may include a turbine disposed in line with the engine's exhaust stream, and coupled via a drive shaft to a compressor disposed in line with the engine's intake air passage. The exhaust-driven turbine may then supply energy, via the drive shaft, to the compressor to boost the intake air pressure. In this way, the exhaust-driven turbine supplies energy to the compressor to boost the pressure and flow of air into the engine. Therefore, increasing the rotational speed of the turbine may increase boost pressure. The desired amount of boost may vary over operation of the engine. For example, the desired boost may be greater during acceleration than during deceleration.
One solution to control the boost pressure is the use of a variable geometry turbine in the turbocharger. A variable geometry turbine controls boost pressure by varying the flow of exhaust gas through the turbine. For example, exhaust gas may flow from the exhaust manifold through a turbine nozzle and to the turbine blades. The geometry of the turbine nozzle may be varied to control the angle that exhaust gas contacts the turbine blades and/or to vary the cross-sectional area of inlet passages, or throat, upstream of the turbine blades. Increasing the cross-sectional area of the inlet passages may allow more gas to flow through the passages. Furthermore, the angle of incidence of gas flowing across the turbine blades may affect the efficiency of the turbine, e.g., the amount of thermodynamic energy captured from the flow that is converted to mechanical energy. Thus, the turbine speed and boost pressure may be varied by changing the geometry of the turbine nozzle.
The design of variable geometry turbines has been modified to yield various desirable results. For example, U.S. Patent Application 2013/0042608 by Sun et al. discloses systems and methods to vary the angle of incidence of gas flowing across the turbine blade by adjusting the cross-sectional area of the passages between adjacent nozzle vanes. Herein, an annular turbine nozzle is provided having a central axis and a number of nozzle vanes. Each nozzle vane comprises a stationary vane and a sliding vane, wherein the sliding vane includes a planar surface in sliding contact with a planar surface of the stationary vane. As such, the nozzle vane may enable a desired angle of incidence and a preferred cross-sectional area of the passages over a range of engine operating conditions.
The inventors herein have recognized potential issues with the approach identified above. For example, the sliding vane(s) may intrude at a high flow area of the inlet passages. In this way, intrusion of leading edges of the sliding vanes may create sub-optimal angles of incidence for the incoming gas and thereby lead to increased aerodynamic flow loss. Moreover, the sliding vane traveling on the planar surface may slide a relatively large distance in the radial direction into the high flow area of the inlet passage, thereby leading to packaging challenges.
Further, the above methods and systems do not address potential shock waves generated during certain engine operating conditions, such as engine braking. During engine braking, the exhaust stream may be constricted, and therefore, shock waves may be generated, leading to strong interaction and excitation on the turbine blades. The shock wave-induced excitation, also referred to as forced response excitation or fluid structure interaction, may be a source of fatigue on the turbine blades and a limiting factor of further increasing exhaust braking power of turbocharged engines.
The inventors herein have recognized the above issues and developed an approach to at least partly address the above issues. As one example, an annular turbine nozzle may be provided, comprising a nozzle vane including a stationary vane attached to a surface of a nozzle wall plate and including a first sliding surface, and a sliding vane including a second sliding surface including a flow disrupting feature in contact with the first sliding surface, the sliding vane positioned to slide in a direction from substantially tangent to an inner circumference of the turbine nozzle and selectively uncovering the flow disrupting feature. In this way, the surface treatment may be exposed during various conditions, such as engine braking, to reduce the intensity of possible shock waves and excitation on the turbine blades.
For example, the first sliding surface of the stationary vane and the second sliding surface of the sliding vane may be cambered surfaces, such that the sliding vane may be positioned to slide along a curved line matching the cambered surfaces of the first sliding surface and the second sliding surface. As such, the sliding vane slides on a curved path defined by a curvature, or cambered line, of the first sliding surface and the second sliding surface. Thus, a desired angle of incidence may be substantially maintained while simultaneously reducing a radial displacement traveled by the sliding vane during various engine operating conditions. In this way, exhaust gas expansion losses may be reduced as compared to a sliding vane and stationary vane having planar sliding surfaces.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Finally, the above explanation does not admit any of the information or problems were well known.